Giant iceberg stuck spinning in ocean trap

Something remarkable happened to A23a, the world’s largest iceberg.

For months now, it has been circling at a point just north of Antarctica while in fact it is running alongside Earth’s strongest ocean current.

Scientists say the iceberg, which is more than twice the size of London, is held in place by a giant rotating water column.

Oceanographers call this the Taylor Column phenomenon — and it’s likely A23a won’t escape its captor for many years.

“Normally you think of icebergs as temporary things; they break off and melt. But not this one,” said polar expert Professor Mark Brandon.

“A23a is an iceberg that refuses to sink,” a researcher at the Open University told BBC News.

The iceberg’s lifespan is well documented. It broke away from the coast of Antarctica in 1986, but then almost immediately became trapped in the muddy bottom of the Weddell Sea.

For three decades, it was a static “ice island.” It didn’t budge. It wasn’t until 2020 that it resurfaced and began drifting again, slowly at first, before plunging north toward warmer air and water.

In early April this year, A23a merged with the Antarctic Circumpolar Current (ACC) — a giant ocean current that moves hundreds of times more water than all the rivers on Earth combined around the world.

The aim is to launch rockets into the trillion-ton iceberg, propel it into the South Atlantic and into oblivion.

Instead, A23a is going nowhere. It’s staying put just north of the South Orkney Islands, rotating counterclockwise by about 15 degrees each day. And as long as it does that, its decline and eventual demise will be delayed.

The A23a has never run aground; there is at least a thousand metres of water between the bilge and the seabed.

It was blocked by a type of vortex first described by a prominent physicist in the 1920s, Sir GI (Geoffrey Ingram) Taylor.

The Cambridge scholar was a pioneer in the field of fluid dynamics and was even brought on board the Manhattan Project to model the stability of the world’s first atomic bomb test.

Professor Taylor has shown how an ocean current encountering an obstruction on the seafloor can – under the right circumstances – split into two separate streams, creating a deep rotating mass of water between them.

In this case, the obstacle is a 100km-wide ridge on the ocean floor called Pirie Bank. The vortex sits on top of the bank, and A23a is currently its prisoner.

“The ocean is full of surprises and this dynamic feature is one of the cutest you’ll ever see,” said Professor Mike Meredith from the British Antarctic Survey.

“Taylor columns can also form in the air; you see them in the movement of clouds over mountains. They can be just a few centimeters wide in a laboratory tank or extremely large, as in this case when the column has a giant iceberg smashing into the middle.”

How long can the A23a spinner continue to perform a spinning motion?

Who knows, but when Professor Meredith placed a scientific buoy on Taylor’s Column above another mound on the east side of Pirie Bank, Floating device still rotating in place after four years.

A23a once again perfectly illustrates the importance of understanding seafloor shape.

Seamounts, canyons, and slopes have profound effects on the direction and mixing of water, as well as on the distribution of nutrients that drive biological activity in the ocean.

And this influence extends to the climate system as well: it is the great movement of water that helps to disperse heat energy across the globe.

The behaviour of A23a can be explained because the ocean floor just north of South Orkney is well surveyed.

Not so in most of the rest of the world.

Currently, Only a quarter of the Earth’s seafloor has been mapped. according to the best modern standards.